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Abstract

"This study developed learning progression-based measures of science teachers' content knowledge (CK) and pedagogical content knowledge (PCK). The measures focus on an important topic in secondary science curriculum using scientific reasoning (i.e., tracing matter, tracing energy, and connecting scales) to explain plants gaining weight and exchanging gases. Using a design-based research approach, we conducted the research in four cycles. The findings reported in this article were based on the data collected in the last two cycles (year 2011-2012 and year 2012-2013). This study contains two parts. First, 194 teachers participated in professional development workshops and completed a teacher assessment measuring CK and PCK. A learning progression-based scoring system was developed for these measures. Second, a subgroup of 25 teachers participated in a teaching experiment. These teachers taught a learning progression-based unit on plant growth and functioning. Their students took written assessments both before and after the teaching intervention. In this process, validity evidence from multiple sources was obtained and analyzed to evaluate the claim that the assessment scores tell how well teachers understand the knowledge essential for teaching the science topic. This validity argument supports our interpretations that led to three results. First, teachers overall performance on CK was a bit higher than PCK, but not significantly different. Second, two challenges confronting teachers are adaptively applying scientific principles and understanding students' intuitive ideas. Third, there was a statistically significant relationship between teachers' measured CK and PCK and students' learning from the plant unit."